1. Field of the Invention
The present invention relates to a toner composition for use in a developer developing an electrostatic latent image formed by electrophotography, electrostatic recording, electrostatic printing, etc., and to a method for manufacturing the toner composition. More particularly, the present invention relates to a toner composition for use in copiers, laser printers, plain paper facsimile machines, etc., and to a method for manufacturing the toner. In addition, the present invention also relates to a color toner composition for use in full color copiers, full color laser printers, full color facsimile machines, which use a direct or indirect electrophotographic developing method, and to a method for manufacturing the color toner composition.
2. Discussion of the Background
An electrostatic latent image formed on an image bearing member, for example, by electrophotography, electrostatic recording, electroprinting or the like method is developed with a developer to form a visible image (i.e., a toner image) on the image bearing member (developing process). The toner image is then transferred onto a receiving material such as receiving paper optionally via an intermediate transfer medium (transfer process). The toner image on a receiving material is then fixed on the receiving material (fixing process).
As the developer, two-component developers consisting of a carrier and a toner and one-component developers which do not include a carrier and which consists of a magnetic or non-magnetic toner are well known. In a two-component developer, the toner is frictionally charged, for example, by contacting the carrier. In a one-component developer, the toner is frictionally charged by contacting a roller supplying the toner to a developing sleeve, a blade regulating the toner to form a toner layer on the developing sleeve and/or the like member.
In order to prepare high quality images, it has been tried that toners having a small particle diameter and/or a narrow particle diameter distribution are used. When such toners are prepared by a manufacturing method using kneading and pulverizing, the particles of the resultant toners have an irregular form. When such an irregular-form toner is used in image forming apparatus, the toner is further pulverized by being agitated together with a carrier, and by contacting a developing roller, toner supplying roller, a toner regulating blade, and a friction-charge applying blade, resulting in formation of toner particles having a very small particle diameter. In addition, a fluidizing agent adhering on the surface of toner particles tends to be embedded into the toner particles, resulting in deterioration of image qualities. Further, since toners having an irregular form have poor fluidity, a large amount of a fluidizing agent has to be added to the toners and thereby image qualities such as background density and fixing property of the resultant toner images are deteriorated and in addition a problem occurs in that the manufacturing costs increase. In addition, when a toner has poor fluidity, the filling factor of the toner deteriorates and thereby a toner bottle in which the toner is filled has to be enlarged in size. Such toners prevent miniaturization of image forming apparatus.
In addition, in full color image forming apparatus, color image transfer processes in which color toner images are transferred onto receiving materials become complex more and more. When toners having an irregular form are used for such full color image forming apparatus, the resultant color images tend to have omissions because the toners have poor transferability. When it is attempted to prevent such image omissions, another problem such that the toner consumption increases tends to occur.
Therefore a need increases for a toner which has so good transferability that high quality images can be formed even when a small amount of the toner is used (i.e., high quality images can be formed at a low running cost). If a toner having good transferability is used, a cleaning unit which is used to remove the toner remaining on the surface of a photoreceptor and an intermediate transfer medium is unnecessary, and therefore the image forming apparatus can be miniaturized and the manufacturing cost thereof can be decreased. In addition, the image forming apparatus has an advantage in that waste toners are not produced. However, in reality it is difficult to perfectly transfer toner images from a photoreceptor or an intermediate transfer medium to a receiving material. Therefore, in reality, toner particles remaining on a photoreceptor or an intermediate transfer medium are removed using a cleaner and the collected toner is reused.
When a spherical toner is used, it is very difficult to remove toner particles remaining on a photoreceptor by a cleaner. Therefore in attempting to provide a toner having a combination of good properties of the toners having an irregular form and good properties of the toners having a spherical form, toners having a slightly deformed spherical form and methods for manufacturing such toners have been proposed.
On the other hand, toner manufacturing methods in which fine toner particles having an irregular form are aggregated to form aggregated toner particles and then the aggregated toner particles are fused to unite the fine toner particles. When the fine particles are prepared by an emulsion polymerization method, resins including units obtained from one or more radically polymerizable monomers such as styrene, acrylic and methacrylic monomers have to be used. However, in view of transparency, flexibility, adhesion to receiving materials, and plasticizer resistance of toner images, it is preferable to use polyester resins and polyol resins as the toner resin. In particular, it is required for full color toners to have good transparency and sharply-melting property. Therefore resin particles obtained by an emulsion polymerization method cannot be used for full color toners.
Japanese Laid-Open Patent Publications Nos. 10-20552 and 11-7156 (hereinafter referred to as JOPs) have disclosed a toner manufacturing method in which a polyester resin solution including a colorant is emulsified in an aqueous liquid and then the particles of the emulsion are coagulated such that the aggregated particles have a toner particle size, and a method in which a fine dispersion of a polyester solution and a fine colorant dispersion are hetero-aggregated.
In general, it is difficult to finely disperse dyes and pigments, which are typically used as colorants, in a solvent which does not dissolve the dyes and pigments. Therefore the resultant toners have poor tinting power. In addition, when hetero aggregation is performed, fine colorant particles in the dispersion do not necessarily aggregate uniformly together with fine resin particles in the dispersion, and it is possible that fine colorant particles aggregate by themselves. Therefore, toners having good tinting power cannot be provided. In addition, when a colorant dispersion is prepared, a large amount of a dispersant is needed and therefore the resultant toner has poor moisture resistance. Further investigation of controlling the dispersion of a charge controlling agent and/or release agent included in a toner has not been performed.
JOP 2-153361 discloses a toner manufacturing method which includes the steps of melting and kneading toner constituents, dissolving (or dispersing) the kneaded mixture in a solvent, and then dispersing the solution (or dispersion) in an aqueous liquid. By using this method, spherical toner particles can be easily manufactured. A colorant such as carbon black can be easily dispersed in a resin by kneading the colorant and the resin upon application of relatively low shear stress. However, when the kneaded mixture is dissolved or dispersed in a solvent, the colorant tends to aggregate again. In addition, it is difficult to disperse organic pigments in a resin when low shear stress is applied. Therefore the resultant color toners have poor coloring property and color reproducibility.
JOP 7-333890 discloses a toner manufacturing method which includes the steps of preparing a master batch colorant by kneading toner constituents, which includes a colorant but not including a binder resin, and a resin which can be mixed with the binder resin upon application of high shear stress; dissolving or dispersing the master batch colorant and a binder resin in an organic solvent; and then dispersing the solution (or dispersion) in an aqueous liquid. However, when the master batch colorant and the binder resin are dissolved or dispersed in an organic solvent, the colorant aggregates therein. Therefore the resultant color toners have poor coloring property and color reproducibility. In addition, other toner constituents such as charge controlling agents and release agents are excessively dispersed in the master batch colorant, and therefore the resultant toner has poor charge property and release property.
Because of these reasons, a need exists for a toner which has good coloring property, color reproducibility, charge properties and releasability.